Power conversion means for radio apparatus



w. L. KRAHL 1,829,226

POWER CONVERSION MEANS FOR RADIO APPARATUS Filed March 10; 1928 2 Sheets-Sheet l Oct. 27, 1931.

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Oct. 27, 1931. w. 1.. KRAHL POWER CONVERSION MEANS FOR RADIO APPARATUS 2 Sheets-Sheet 2 Filed March 10, 1928 ATTORNEY Patented Oct. 27, 1931 UNITED STATES PATENT OFFICE WALTER LOUIS KR AI-IL, OE MONTCLAIR, NEW JERSEY, ASSIGNOR T0 ARCTUR'U'S RADIO TUBE COMPANY, OF NEWARK, NEIV JERSEY, A CORPORATION OF DELAWARE POWER CONVERSION MEANS FOR RADIO APPARATUS Application filed March 10, 1928. Serial No. 260,747.

This invention relates to a means and a method for converting direct current operated radio sets to alternating current operation and more particularly, to such alternating current operation with the use of tubes of the heater type.

One of the objects of the invention is to provide a means whereby alternating current tubes of the heater type may be used in a radio set designed for direct current operation without changing any of the perma nent connections of the set. I

Another object of the invention is to provide a method of easily and quickly converting a direct current radio set to alternating current operation where the grid leak of the set is in an inaccessible place.

Another object of the invention is to provide means whereby alternating current tubes of the heater type may be used in a radio set designed for direct current operation without changing any of the permanent connections of the set and the grid return from the tubes may be connected to a point on the heater circuit having substantially cathode potential.

Other objects of the invention will be apparent as the description'thereof proceeds.

One embodiment of the invention has been illustrated in the accompanying drawings, in which:

Fig. 1 is a circuit diagram of a radio set embodying the invention;

Fig. 2 is a perspective view of the harness used for connecting the tubes;

Fig. 3 is a sectional elevation of a tube showing the manner of attaching the harness thereto; and

Fig. 4 is a side view of the base of the tube shown in Fig. 3; and

Fig. 5 is a circuit diagram of another form of radio circuit to which the invention is applicable.

In my co-pending application, Senal No. 239,027, thermionic tubes and method and means of connecting same filed December 10, 1927, I described and illustrated a means of connecting alternating current tubes of the heater type to a set originally designed for direct current operation in which I disconnected the grid return end of the grid leak and connected said end to a positive potential while the original grid return of the circuit was connected to a negative potential.

This was done by placing an insulating connector between the end of the grid leak and the support therefor which was connected to the positive terminal of a D battery and thus the outer end of the grid leak was insulated from the coil of the grid circuit and' the grid of the detector tube was given a positive bias. This method of connecting the alternating current tubes is very satisfactory but in converting some radio sets it has been found very diiiicult to place the necessary insulating conductor over the end of the grid leak in order to insulate it from the original grid return of the circuit and give it a positive potential. The present invention, therefore, is intended to be used in such cases but may be used in others, if desired,and is adapted in certain instances, to change the rectification of the set from the usual grid leak and condenser to plate rectification.

convert the set into an alternating current operated set, while certain alternative changes are indicated in dotted lines. One

radio frequency amplifier tube I, a detector tube II and two audio frequency tubes III and IV are shown. The grid leak 1 and condenser 2 are connected to the grid of the detector tube II and through the lead 3 to the positive filament lead of the detector tube. The grids of the audio frequency tubes III and IV are connected toground through the O batteries 5 and 6 respectively and the grid of the radio frequency tube I is directly connected to ground as indicated.

It is preferable,'in using alternating current tubes, to provide an independent heating circuit without any rheostats, potentiometers or other reactance devices in the circuit, and hence I provide a pair of wires 10 and 11 which are adapted to be connected to the heater terminals 12 and 13 of each tube and tothe secondary coil 140i a stepdown transformer 15 which hasits primary coil 16 connected to a source 17 of alternating current. A convenient way of attaching these. wires to the alternating current tubes is illustrated in Figs. 3'and 4. A-tube 18 is provided having a special base.19 in which are secured standard pins adapted to enter. the. openingsin the socket but in which.

thefilamentleads' 20 and 21 are not connected to the filament pins 22 but are-brought out through holes 23 in the side of the base and soldered or otherwiseconnected to small,

plates 24 which may be provided with holes '25 through which a screw 26 may be threaded into'a tapped hole 27 in the side of the base.

Theheater current wires 10 and 11 therefore, may be attached by means of short leads 29 j and 30 respectively, directly to these screws,

care being taken that the terminal A on each tube which is connected to the cathode inside of the tube is connected to a single one of the heater current wires in this instance designated as 11. It is desirable to connect the" grid return'to the heater circuit at a point having as near as possible cathode potentiala-nd, therefore, this grid return is preferably connected to the wire 11, connecting the filament terminals which also form the cathode leads,

In many'in'stances it is suflicient merely to'connect this grid return toa' point on to,fhut inisome' instances where amplification the heater current wire 11 adjacent its connection with the detector tube of the set, as is ill ustrated in theapplication above referred "is" very efficient a hum may be produced due to thecommon cathode and heater current lead from the point ofconnection; up to the cathode in the tube. I therefore, have found \1 it: expedient to-provide a, means for connecting the grid return to ,apoint having exactly cathodepotential or so near cathode potential that the hum otherwise produced by the: drop in alternating current potential in the com- -mon cathode and heater current lead will be negligible. This maybe accomplished by connecting a high resistance across the heater 7 current leads, and then connecting the grid return to a point on this resistance, between which and the end of the; resistance nearestthe" cathode, there will be an alternating curr rent drop which will bala'ncethe alternating 5 current-drop'in thecommon cathode and heater lead. Such a deviceh'as been eX- plaine'd and described in my co-pending- 'application entitled Compensating device and method of compensating for hum in alternatin'gicurrent'tubes, Serial No. 243,501. As

' described inthe said application, a convenlent method, of connecting this resistance across the circuit is to provlde a high resist ance of about one thousand-ohms and a potent'iometer or rheostat of about'one ohm. If

nected to a cable 32 which forms a harness to be applied to any radio set where it is desired to convert the set from direct current to alternating currentoperation. :The cable '32 contains-three wires, two of which are the heater currentleads 10 and 11 which are preferably twisted together and are-provided.

with the short leads 29 and 30 spaced along their lengths at convenient intervals so that they may be connected to the tubes, and the third wire 33 is connected to the wire 11 by means of the resistance 34 and potentiom-..

eter, 351which are connected across'the leads 10 and 11 ass-indicated in Figs. v1 and 2, the connections being made at points ad acent the detector tube of the set.

In most radio sets using grid leak and con-, denser rectification the leak is shunted between the grid and cathode and the condenser is connected -1n serles with the C011 as illustratedin Fig. 5 of the drawings. When the grid leak and condenser are thus arranged and the grid leak is in an inconvenient location, the necessity of making'the connection to one end of the grid leak may be avoided by changing the circuit to plate rectification.

To do this it is necessary to remove the grid;

leak and short circuit the grid condenser so that apositivepotential may be placed on the grid, where the grid leak is-connected around the condenser as is illustrated in Fig.

1; The object of the invention maybe real ized by using either grid leak and condenser or plate rectification depending on the particular circuit being changed. 7 i s When the A battery terminals oftheD. C.

set are not connected together by a potentiometer, it is convenient to use the A minus terminal or lead as the G minus lead of the converted receiver and the A plus lead asthe D plus lead. Thus in Fig. 1 there is no potentiometer and the detector grid returng} is connected to the positive filament lead whereby the A minus terminal of the set may be connected to the minus terminaleof the 0 battery as shown'while the'A-plus lead may be used for the positive D; potential anch connected to a '1) battery 36? as shown in dotted lines. In this case thewire 37 shown dotted across the grid leak 1 and condenser 2 would not be used, grid leak and condenser rectification being used. v

In most receivers, the A plus terminal is connected to the plus filament terminal of each tube and the grid leak or both the grid leak and the detector grid return are connected to the plus terminal of the detector. If, however, the grid leak is connected to the negative filament terminal as is done in rare instances or if a potentiometer connects the A battery terminals the A leads cannot be used for the C negative and D positive supply. In this case I have found it expedient to short circuit the grid leak and condenser as shown by the dotted line 37 of Fig. 1, and give the detector grid 2. negative potential by connecting the A terminals of the set together with a wire 3 as shown by the dot and dash line. No D battery need be used with this connection.

In converting a set, therefore, and making use of this invention, it is only necessary to remove the direct current tubes from the set; short circuit the grid leak and condenser or not depending on the circuit, or short circuit the grid condenser and remove the leak if the circuit is similar to 5, and insert alternating current tubes to which the harness has been attached. The potentiometer may then be mounted in any desirable position either inside or outside of the set, the wires leading thereto being of sufficient length to meet the necessities of each individual case or the desires of the set owner. The grid return lead or leads from the various tubes should then be connected, in the case shown by means of the A minus lead, to the negative terminal of a C battery 36 of from about one and one-half to three volts, the positive terminals of which should be connected to the negative terminal of the B battery, as indicated. As the A negative terminal is grounded in the circuit shown, this connects the negative bias to the grids of the tube through ground. It will be noted that the B minus terminal 4 of the set is not used at all.

A voltage of about twenty-two and one half volts should be applied to the detector tube and the voltages for the plate circuits, of the other tubes should be in accordance with standard practice, whereupon the set is ready for operation. Where two or more grid returns including that from the detector tube are connected to a common lead, the plate voltage of the detector tube should preferably not exceed twenty-two and one half volts for a negative grid bias up to three volts but where the detector grid circuit is independent, or can be easily made so, it may be desirable to apply a higher plate voltage in which case the negative grid bias on this tube alone may be increased. For instance for a grid bias of six volts negative, on the detector tube, a plate voltage of 45 volts was found to give good results.

In some receivers it may be desirable to use a by-pass condenser 38 (Fig. 1) of about one micro-farad capacity between the cathode of a radio frequency tube and ground to prevent oscillation which may be produced by the long grid leads i. e., through the A minus lead to the negative C battery terminal and back to the cathode of the tube. In the D. C. circuit the grid return has a short path to the negative filament terminal.

It will be evident from the above description that I have provided a means and a method for converting a direct current radio set to alternating current operation, whereby such conversion may be made when the grid leak is in an inaccessible place and which is simple, easily applied and accomplished, so that a direct current set may be changed over to alternating current operation in a minimum time.

While I have shown and described certain embodiments of the invention, I do not desire to limit myself to the specific construction shown and described, as many changes in construction may be made without departing from the spirit of the invention, but I desire to interpret the invention broadly, limited only by the appended claim.

Having thus described my invention, what I desire to claim is:

A means to convert a direct current radio set to alternating current operation which comprises a cable, a pair of wires in said cable adapted to be connected to the heater terminals of alternating current tubes, a relatively large resistance connected to one of said wires, a relatively small resistance connected between the end of said first resistance and the other of said pair of wires, a third wire connected to a point on said small resistance, and means to vary the resistance to which said wire is attached.

In testimony whereof, I aflix my signature.

WALTER LOUIS KRAHL. 

